To me, I've always felt the reason Sonny hasn't said anything about Gabi's transgressions to Will is simply because Will won't listen. He's too loyal (Chad mentioned it while he and Sonny were decorating the coffee house Christmas tree a few months back). If Will's not in an emotional place to listen, and Sonny presses the issue, all that's gonna happen is that WilSon communication will shut down and Sonny will come off as the current whining about the ex. I don't have the show memorized but, off the top of my head, I can't think of a moment when Sonny could have said anything. I do think, however, Sonny should have pushed Chad to say something to Will himself.